after executing execvp()... program hangs up

Applications Programming
1

Hi ,

I m actually trying to implement pipes program,but after executing the execvp(),my program is getting hanged up :mad:

Actaully i m getting the desired output expected from execvp()...but once results are displayed on the output screen ,program is getting hanged up

values of variables before execution of this code

intial_command=more
argList[0]=more
argList[1]=NULL

child code:

{
close(0);
dup2(pipes[0][1],0);
close(pipes[0][0]);
execvp(intial_command,argList);
}
parent code:
printf("after child");
waitpid(pid,&status,0);

i guess since i have closed the stdin using close(0) thats y i m not able to input anythng even after execvp()...but as far my knowledge once the execvp() functions gets executed the child process gets terminated..so my program should resume to parent process

2 
close(0);
dup2(pipes[0][1],0);
close(pipes[0][0]);open(0);
execvp(intial_command,argList);

Isn't that open(0) giving you any errors during compilation? The open syscall needs atleast two arguments.

3

BTW it wasnt giving any system error...dunno kno how :rolleyes:

4

execvp does not create a new process. It replaces the current process.

Proper sequence of events would be:

  • fork() to copy current process. The new process will be identical to the old one with one differnce -- the child and parent get different return values from fork().
  • Close and/or rearrange file descriptors as you please in the child code to make whatever the stdin/stdout/stderr/etc.
  • Call execvp in the child process

Maybye you're using fork already, but that code snippet doesn't show it..